This application claims the priority of German patent document 199 19 675.3, filed Apr. 30, 1999, the disclosure of which is expressly incorporated by reference herein. The invention relates to a system for automatically controlling operation of a vehicle.
German patent document DE 41 18 332 A1 discloses a system for controlling a vehicle driving device which is intended to relieve the burden on the driver in stop-and-go operation on overcrowded roads. In stop-and-go operation, the motive power of the vehicle is controlled automatically so that the current vehicle speed makes a transition to a predetermined target speed. If the driver actuates the brake pedal, the motive power is automatically interrupted. If the driver releases the brake pedal, the vehicle resumes the target speed.
It is, of course, possible with such a control system to move the vehicle exclusively by actuation of the brake pedal in stop-and-go operation. However, this assumes that the target speed (which the vehicle is not to exceed in congested traffic) is specified by the driver. Because the traffic situation is normally continuously changing, in order to avoid critical situations, the driver is forced either to concentrate harder on the traffic and, if appropriate, actuate the brake pedal to prevent the vehicle from accelerating unintentionally to a high target speed not suitable for the current traffic situation, or the driver must continuously adapt the target speed to the current situation. In both cases, the aim of relieving the burden on the driver is not adequately achieved.
One object of the invention is to provide a simple and inexpensive control system which minimizes the burden on the driver of a motor vehicle, and allows reliable control of the vehicle in dense traffic.
This and other objects and advantages are achieved by the control system according to the invention which embodies the fundamental premise that the driver must actively take the initiative to move the vehicle, and if he or she does not, a brake servo device is automatically switched on, braking the vehicle. (This is referred to herein as the xe2x80x9cacceleration by the driverxe2x80x94automatic braking mode.xe2x80x9d)
The procedure according to the invention also has the advantageous feature that the xe2x80x9cacceleration by the driverxe2x80x94automatic braking modexe2x80x9d is not initiated, and the vehicle cannot be braked automatically without the implementation of a predefined vehicle operation pattern by the driver (as discussed hereinafter), thereby increasing safety in the case of incorrect responses by the driver, e.g. a delayed reaction. Another important advantage is that the driver is not compelled to enter commands, such as target values, into the control system.
The control system according to the invention is particularly suitable for driving in congested traffic.
Adaptation to the traffic situation is performed by actuation of the accelerator pedal, which is to be carried out by the driver, thus eliminating the need for any additional, expensive measures or devices for correction of the system to match the traffic. At the same time, safety is increased by the automatic brake actuation if the accelerator pedal remains unactuated, thereby compensating for lack of response or excessively late responses by the driver.
The xe2x80x9cacceleration by the driverxe2x80x94automatic brakingxe2x80x9d mode is triggered automatically by detection, in a detection device of the control system, of a defined actuation of the brake pedal corresponding to a predetermined braking scheme. Automatic triggering of the xe2x80x9caccelerationxe2x80x94automatic brakingxe2x80x9d mode, which is suitable, in particular, for stop-and-go operation, has the advantage that the driver does not have to consciously trigger the ideal mode for driving in congested traffic; instead, the system detects congested traffic automatically. Moreover, there is no need for forward-looking sensors, (e.g., radar or optical detection units), to detect vehicles travelling ahead. A device which detects the current position of the brake pedal is sufficient to detect congested traffic.
The xe2x80x9caccelerationxe2x80x94automatic brakingxe2x80x9d mode is advantageously triggered if the brake pedal is actuated at least twice in succession within a defined period of time, preferably if the vehicle is decelerated to a halt in each individual braking operation and the brake pedal is released between the two braking operations. This braking scheme can be employed as a reliable trigger criterion and accidental unintentional triggering can be reliably excluded since the trigger conditions have been specified with sufficient accuracy to eliminate confusion with other traffic situations, such as braking to a halt at a traffic light.
In a preferred development, a brake pressure which results in a desired deceleration characteristic curve of the vehicle is built up during the braking phase in the xe2x80x9caccelerationxe2x80x94automatic brakingxe2x80x9d mode. The deceleration characteristic curve or function can be chosen so that stopping can be performed in a particularly comfortable manner. In this context, it is possible to allow for longitudinal elasticity of the vehicle in such a way that longitudinal vibrations at the moment of stopping are minimized.
It is advantageous if the brake pressure is also maintained even when the vehicle is stationary if the accelerator pedal remains unactuated, in order to ensure the maximum degree of reliability. It is also possible in this context to allow for the slope of the road by adjusting the brake pressure in accordance with the slope of the road in such a way that the vehicle remains stationary. In addition (or as an alternative) to the actuation of the wheel brake, it is also possible to activate a parking brake when the vehicle is stationary. Activating the parking brake offers the advantage that a braking force which immobilizes the vehicle can be produced irrespective of the vehicle state. Thus, it is possible, in particular, to immobilize the vehicle even when the internal combustion engine is switched off and/or if the driver gets out.
As a trigger condition for cancelling the xe2x80x9caccelerationxe2x80x94automatic brakingxe2x80x9d mode a vehicle state variable is preferably checked to determine whether it exceeds a predetermined limiting value. Suitable vehicle state variables in this context are, in particular, the vehicle speed and/or the steering-wheel angle. These state variables are usually available in any case for further control interventions which stabilize the vehicle.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.